Radio communications systems are used for transmitting information, voice or data, by electromagnetic waves via a radio interface between a transmitting radio station and a receiving radio station. One example of a radio communications system is the known GSM mobile radio network, whose architecture is described, for example, in B. Walke, “Mobilfunknetze und ihre Protokolle” (Mobile radio networks and their protocols), Volume 1, Teubner Verlag Stuttgart, 1998, pages 139 to 151. In this case, a channel formed by a narrow frequency band and a time slot is provided for transmitting each subscriber signal. Since a subscriber signal in one channel differs in frequency and time from the other subscriber signals, the receiving radio station can detect the data from the subscriber signal. In more recent radio communications systems, such as the UMTS system, the individual subscribers are furthermore distinguished by different spread codes.
A radio communications system, for example a GSM mobile radio network, has a large number of mobile switching centers which are networked to one another and provide access to a landline network. Furthermore, the mobile switching centers are each connected to one or more base station controllers. The base station controller allows a connection to at least one base station, and manages the radio resources of the connected base stations. Such a base station is a transmitting/receiving unit, which can set up a radio link to mobile stations via a radio interface, which is also referred to as an air interface.
A region which is covered by a radio communications system is subdivided into individual radio zones, which are also referred to as cells. A cell is in this case controlled by one of the base stations, via which radio links are set up from mobile stations which are located in this cell. In order to avoid interference with radio links in adjacent cells, each cell is assigned a subset of physical channels which are available in the radio communications system. Directly adjacent cells use different physical channels, via which radio links are set up between a mobile station and the base station. Physical channels are reused only when two cells are at a certain distance from one another.
If a mobile station moves from the region of one cell to another cell, then an automatic handover procedure is carried out during the course of the radio link, so that an active radio link can be maintained even beyond cell boundaries. In the handover procedure, the radio link between the mobile station and the radio communications system, which is set up via a first transmitting/receiving unit, is switched to a second transmitting/receiving unit. The need for such a handover procedure is identified by the radio communications system.
It has been found that handover procedures can lead to overload messages at the operation and maintenance center with regard to the connection between the base station and the base station controller and to use of all the channels which are required to set up new radio links via a base station. The latter situation leads to requests for setting up a new radio link being rejected.